Retrievable density control valve

ABSTRACT

Retrievable valve apparatus for lightening oil being gas lifted through a tubing string. The apparatus includes a valve body having a fishing neck which projects upwardly within the tubing string and valve means proper carried by the body for selectively communicating the tubing string interior with a pressurized gas supply to inject gas into the oil upwardly past the fishing neck in response to a predetermined pressure of oil lifted in the tubing string above the apparatus, the valve body being provided with a port to pass the pressurized gas into the body when the body is selectively positioned within the string.

United States Patent TUBING RICIPROCA Thompson 1 July 1 1, 1972 I54]RETRIEVABLE DENSITY CONTROL 3,045,159 7/1962 Garrett et all ..137/1s5VALVE 2,275,345 3/1942 3,016,844 1/ 1962 [72] Inventor: George L.Thompson, 3265 W. Andrews 3 0 2 0 5 7 19 2 St., Fresno, Calif. 93705 0Primary Examiner-James A. Leppink [22] Flled' 1970 Attomey-White,Haefliger& Bachand [21] Appl. No.: 80,340

[57] ABSTRACT [52] US. Cl......; ..l66/224, 137/155, 417/86, R ll'i flValve pparatus for lightening Oil being gas lifted 417/117 through atubing string. The apparatus includes a valve body 1 1m. 1721! 33/00having a fishing neck which projects upwardly within the tub- [58] FieldofSearch ..166/224; 137/155; 417/86, 108-118 mg t s and valve means P 1earned y the y for selectively communicating the tubing string interiorwith a Ci pressurized gas supply to inject gas into the oil upwardlypast [56] References M the fishing neck in response to a predeterminedpressure of oil UNU'ED STATES PATENTS lifted in the tubing string abovethe apparatus, the valve body being provided with a port to pass thepressurized gas into the 2,145,918 2/1939 Bryan ..417/1 12 body when thebody i selectively positioned within the string 3,375,847 4/1968 Brown2,314,869 3/1943 Boynton ..137/155 10 China, 8 Drawing Figures SHEET 10F3 P ATENTEDJHL 1 1 I972 IZ/OMPSO/V M? Mud INVENTO/Q POWER 6A5 OUTPUTmeme 1 RECIPROCATO a v I. I v vi 1 r l 1 iii. I Q e M u 7 11 P 7 x r 1PATENTEDJUL 1 1 m2 75, 4

SHEET 3 0F 3 1&0. 4.

I N vs/vro/z 650265 I 11/014 50 1 RETRIEVABLE DENSITY CONTROL VALVEBACKGROUND OF THE INVENTION 1. Field of the Invention This invention hasto do with apparatus for lifting oil from wells and more particularly,with density control valve apparatus and fluid handling systemsincorporating the apparatus for the efficient removal of oil from wellssuch as those requiring a gas lift assist to bring oil to the surface.

The removal of oil from wells has been accomplished by pumping eithermechanically or by gas injections into the oil to carry the oil to thesurface. In U.S. Pat. No. 2,416,359 to Thompson and Cejka, a gas lifttype of pumping operation is described in which gas is injected into areciprocating inner tubing string, provided with a valve mechanism toreceive and transport oil from the depths of a well to the surface underapplied gas pressure.

2. Prior Art Gas lift pumps typically employ an inner and outer tubingstring or well casing between which gas is forced at a suitable pressureto lift discrete quantities of oil to the surface. As the well depthincreases and bottom pressure decreases with depletion of the pool, theweight of oil within the tubing string may be such that gas pressureeconomically available is not efficient or even adequate to lift the oilslugs to the surface.

In these cases, it has been known to provide means for lightening theoil being lifted by injection of gas thereinto in the course of itsupward travel. Means for doing this are termed density control valves.In the patent referred to above, a density control valve is shown fixedto the inner tubing wall by couplings providing for the delivery ofpressurized gas into the valve for injection into the lifted oil inresponse to predetermined weight conditions in the oil.

In practice, the volume of gas injected by the density control valve isdesirably varied with changes in bottom conditions; moreover, the valveseat may wear requiring repair. In either instance, with previouslyknown gas control valves, e.g. U.S. Pat. No. 2,416,359, it has beennecessary to pull the inner tubing string to replace, repair or adjustthe gas density control valve. While pulling the string is at best aconsiderable inconvenience, in the deep wells now being operated, theeffort and downtime required for so doing is likely to be economicallyprohibitive.

SUMMARY OF THE INVENTION Accordingly, it is a major objective of thepresent invention to provide a density control valve apparatus which isretrievable from the tubing string for replacement, modification orrepair and replaceable in the tubing string without pulling the tubingstring, and which particularly introduces gas into the inner flowingstring in an upward direction. The valve finds particular usefulness inconnection with gas lift pump apparatus in which the inner tubing isreciprocated in pumping oil to the surface with gas supplied to theinner tubing through a gas lift valve.

Specifically, the invention provides a retrievable valve apparatus forlightening oil being gas lifted through a tubing string including abovethe oil supply level, a valve body having a fishing neck adapted toproject upwardly within the tubing string and valve means carried by thebody for selectively communicating the tubing string interior with apressurized gas supply to inject gas into the oil upwardly past thefishing neck in response to a predetermined pressure of oil lifted inthe tubing string above the apparatus. The valve body is provided with aport to pass the pressurized gas thereinto when the body is selectivelypositioned in the tubing string. The valve body may carry laterallyprojecting means below the fishing neck for supporting the apparatus inthe tubing string and may be provided with an internal bore communicablewith the body port, e.g., plural upwardly diverging passage meanscommunicating the bore with the exterior portion of the body, whichportion may be annularly recessed, located adjacently below the fishingneck. There may further be in- I'Lll cluded an actuator for the valvemeans comprising an axially movable piston responsive to lifted oilpressure to move downward and to gas supply pressure to move upward,both relative to the fishing neck, the actuator thus being responsive topressure differences between the oil and pressurized gas supply toactuate the valve means. Added downward pressure may be derived fromresilient means arranged to downwardly bias the piston.

The retrievable valve apparatus of the invention may be mounted on amounting means fixed within the tubing string to locate the apparatusopposite a tubing port, the mounting means typically comprising a sleeveadapted to sealably receive the apparatus in such fishing neckprojecting relation that the neck is accessible above the sleeve, andported between the valve body port and the tubing port for passage ofpressurized gas from without the tubing into the valve body interior.The mounting sleeve may be annularly recessed opposite the annularrecess in the valve body and passage outlet and apertured to pass fluidfrom the body bore into the tubing string. The valve body port typicallyis in open communication with the gas supply; and communicable with thebody port, there may be provided an axial gas passing bore. Between thebody port and the body passage, a valve seat is typically provided,encircling the body bore. A needle valve is provided below the borecomprising a stem pointed end having a portion which normally engagesthe valve seat against fluid passage, and also having a valve stemactuator comprising a piston fixed on the stem and movable axiallywithin the valve body relative to the fishing neck thereof, a firstpressure port for communicating lifted oil pressure around the sleeve tothe piston upper surface and a second pressure port for communicatinggas supply pressure outside the tubing to the piston lower surface, saidpiston being responsive to superior force on its upper surfaceoptionally enhanced by a compression spring centered on the valve stemand engaging the piston in downward biasing relation to unseat the pointstern portion and to permit supply gas to flow through the bore into thetubmg.

The valve apparatus is useful in connection with apparatus for liftingoil from a well by gas under pressure through a flow string, e.g., theinner string of spaced concentric tubing strings which may be adapted tobe reciprocably movable within the well, the apparatus including meanscarried at the lower end of the inner string adapted to receive oil,e.g., in response to reciprocation of the inner string to be lifted tothe surface through the inner string under pressure of gas surroundingthe flow tubing string and at a density controlled by the retrievablevalve apparatus described above located within the inner tubing forselectively introducing gas into the flow string. In this embodiment ofthe invention, pressurized gas is provided between the tubing strings.The mounting sleeve, fixed within the inner tubing string and opposite aport therein, serves to communicate the body port with the gas. Thevalve body may be provided with a central vertical fluid passing borecommunicable with the body port and upwardly divergent passagescommunicating the bore with passage outlets above the upper end of thebore at the exterior valve body portion adjacently below the fishingneck, with the sleeve being apertured in a manner to form a linearcontinuation of said passages to smoothly pass fluid from said boreupward into the tubing string radially of said fishing neck. Theapparatus may further include upper and lower sets of circularly spacedsupports supporting the mounting sleeve at vertically spaced locationsand centrally within the inner tubing string, plural members of eachsupport set being ported and alined outwardly with inner tubing portsand alined inwardly with sleeve and body ports to provide fluidcommunication therebetween. Upper and lower annular seals may beprovided between the valve body and the sleeve, the lower seal beinglocated between the first and second pressure ports and the upper sealbeing located between the first pressure port and said body port.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be furtherdescribed as to an illustrative embodiment thereof in connection withthe attached drawings in which:

FIG. 1 is a view in section of apparatus according to the invention withthe gas lift valve mechanism shown in the ejection cycle;

FIG. 2 is a view like FIG. 1 showing the gas lift valve mechanism in theloading cycle;

FIG. 3a and 3b together comprise an enlarged vertical sectional view ofthe density control valve with the upper portion thereof shown in FIG.3a and the lower portion in FIG. 3b, the valve is in the closedposition;

FIG. 4 is a view like FIG. 3b with the density control valve shown inthe normal open position;

FIG. 5 is a cross-sectional view taken on line 5-5 13 in FIG. 3b;

FIG. 6 is a cross-sectional view taken on line 6-6 in FIG. 3b; and

FIG. 7 is a view like FIG. 1 of an alternate embodiment of the inventionapparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference now to thedrawings in FIGS. 1 and 2, a simple, cased single well arrangement isdepicted. Well bore 1 carries a common form of well casing 2. The casing2 extends downwardly into the well bore 1 from a suitable casing landinghead 3 provided at the surface or top of the well. The casing 2 isprovided opposite the oil bearing formation stratum 4 with a perforatedsection or line 5 which admits well fluid into the well casing, so thatit is available tobe removed by the apparatus provided.

The casing landing head 3 is joined to the upper end of the casing 2 andsuch as to provide a landing for outer tubing string 7. Concentric innertubing string 8 which is the flow string in the apparatus, is suspendedfrom tubing reciprocator 9 supported above the casing head 3 by stand 6.Reciprocator 9 is adapted to reciprocate inner tubing string 8. Whileshown diagrammatically, the reciprocator 9 may be an hydraulic pistonconnected to inner tubing string 8 for alternately raising and loweringthe inner string within the outer string 7, as more particularlydescribed in US Pat. No. 2,416,359 mentioned above, which patent isincorporated herein by reference. Reciprocator 9 operation is atintervals and may be controlled by a clock timed intermitter (notshown). The reciprocation movement of the inner flow string 8 is for thepurpose of actuating slide valves 17 and 18 to control the admission ofpower gas supplied to annulus 11 between inner tubing string 8 and outertubing string 7 through conduit 12, leading from a compressor or othersource (not shown) of gas under pressure from the annulus to the pumpchamber 13. Pump chamber 13 comprises the lower portion of outer tubing7 below the working barrel 10. The pump chamber 13 is of a diameterlimited by the inside diameter of the outer casing 2 or perforated liner5 but may be as long as required or desired to hold a capacity toproduce the well at a desired rate determinable by the standing level offluid in the hole and the productivity index of the formation at 4surrounding the perforated liner 5.

Eductor tube 14 hangs inside the pump chamber 13 and its internalcapacity comprises part of pump chamber 13; it has its open end near thebottom standing valve 15 and is attached at its upper end to the innerflow string 8 to move with it.

The portion 10 of the outer tubing 7 immediately above the pump chamber13 forms a working barrel for upper slide valve 17 and lower slide valve18. The upper slide valve 17 controls the flow of power gas to the pumpchamber 13. With reference to FIG. 2, inner flow string 8 is in the downposition, the upper slide valve 17 is sealed within working barrel 10,shutting off flow down through annulus 11 of power gas to the pumpchamber 13. The lower slide valve 18 is in lowered position to unblockvent windows 20 in the center portion of working barrel 10. Verticalchannels 21 are provided in the lower slide valve 18 to provide gaspassageways through the lower slide valve regardless of valve positionin the working barrel lower portion 16. Venting check valve 22 islocated in the upper reaches of the eductor tube 14 to vent the eductortube when the inner tubing string 8 is down, as shown in FIG. 2, thusenabling filling of the eductor tube with well fluid. Check valve 22opens into the pump chamber 13 between the eductor tube 14 and theportion of outer tubing 7 defining the pump chamber 13.

When the flow string 8 is in the lowered position (FIG. 2) the power gasis blocked, as described above, from the pump chamber 13 by the positionof upper slide valve 17. In the absence of power gas in the pump chamber13, the venting check valve 22 is free to open. The vent windows 20unblocked by virtue of the lowered relative position of lower slidevalve 18 are open to the annulus 23 defined outwardly by the casing 2which now contains oil and gas at formation pressure. Pump chamber 13accordingly fills by submergence in the accumulated fluid in the casingthrough bottom standing valve 15 to commence the loading cycle.

The loading cycle is timed by the mentioned clock intermitter or otherdevice so that the pump chamber 13 will just fill before thereciprocator 9 lifts the flow string tubing 8. Upward movement of theflow string tubing 8 causes lower slide valve 18 carried thereby tofirst close vent windows 20 to annulus 23. Sequentially upper slidevalve 17 is moved upwardly and out of working barrel 10 which permitsflow of power gas downwardly through annulus 11 and lower slide valvechannels 21 into the top of pump chamber 13. The gas pressure within theouter portion of pump chamber 13 closes venting check valve 22 as theformation pressure thereon is overcome. Similarly, lower standing valve15 closes by virtue of pump chamber 13 becoming full or from pressuretherewithin. The fluid within pump chamber 13 is thus forced upwardly inthe eductor tube 14 past upper standing valve 24 and into the lower endof flow string 8 (see arrows, FIG. 1), whereupon the lifting apparatus,i.e., reciprocator 9, may be recycled to displace another slug orpumping chamber-filling quantity of well fluid into the lower reaches ofthe flow string tubing 8, by lowering this tubing string to vent thepump chamber 13 as above described, to permit filling with well fluidwhich has again accumulated through the casing perforated section 5.

This pumping cycle may be repeated at any desired rate, e.g., to haveseveral slugs of production fluid in transit to the surface at any onetime, enabling characteristically high production rates with theapparatus described.

The well fluid lifting apparatus thus far described is conventional. Inthe use thereof there may be employed a density control valve 25 locatedin the lower reaches 26 of the flow string tubing 8 for the purpose ofallowing a determined amount of gas to enter the flow string interior 27laterally from annulus 11 between tubing strings 7, 8, so as to lightentoo heavy weights of production fluid in the flow string 8 and inresponse to a predetermined differential of between the flow string 8interior pressure at the valve 25 and the power gaspressure in theannulus l 1.

The density control valve 25 of the present invention is a departurefrom valves heretofore employed for like purposes of lightening fluidproduction. Particularly this valve discharges its gas in an upwarddirection assisting the upward travel of the fluid being pumped upwardlyfrom pump chamber below. Also the present density control valve is aretrievable apparatus, locatable from a distance, i.e., above ground,within a flow string and removable therefrom by wire line withoutpulling the string from the well.

With reference to FIGS. 3a and 3b, which depict a single retrievablevalve apparatus according to the invention, it will be seen that thedensity control valve apparatus of the invention includes a valve body28 having an upwardly, freely projecting fishing neck 29 of slightlylesser diameter than the valve body and carrying suitable annular ribs30 adapted for engagement with a wire carried retrieval tool (notshown). A

laterally projecting latch 31 such as a Type R latch is secured to thefishing neck 29 for the purpose of supporting the valve body 28 inplace. Below the fishing neck 29, the valve body 28 comprises pluralsections in pin and box threaded connection including a two part upperannular section 32 defining an axial vertically extended bore 33 andplural upwardly divergent passages 34 communicating the bore withexterior annular portion 35 of the upper valve body section adjacentlybelow the fishing neck. The valve body section exterior portion 35 isannularly recessed as shown at the level of passage outlets 36 above theupper terminus 37 of bore 33. Upper recess edge 38 is beveled to providea smooth continuation of the flow path through passages 34, outwardlyfrom the valve body 28 and upwardly through ports 81 into flowingannulus 27 carrying production from pump chamber 13 below.

A valve seat 39 is provided in the lower part of the upper annularsection 32 of the valve body 28 at the lower terminus 40 of the bore.Valve seat 39 is provided with a restricted opening 41 selected toprovide the desired control over gas passage ,through the valve openingwhen wide open and is replaceable by disconnecting the lower part ofannular section 32 and the coupling 42 to vary the restriction on gasflow into the bore Coupling 42 comprises a body 43 having a centralannular recess 44 and radial ports 45 adapted for communication withpower gas in annulus 11 as will be described below leading from therecess into an axial bore 46 which is suitably of the same diameter asbore 33 in upper and lower parts of upper annular section 32 spaced frombore 46 across the valve seat 39. Bore 46 in the coupling is adapted toreceive valve stem 47 from below carrying at its upper end abovelabyrinth sealing rings 48, a pointed terminal 49 configured as a needlevalve to seat fluid tightly on seat 39 around valve opening 41.

Below the coupling 42 to receive and guide valve stem 47 there isprovided guide block section 50 of the valve body. Guide block section50 comprises an elongated cylinder having formed therewithin adownwardly stepped axial bore 51 in which valve stem 47 reciprocates tooperate the stem pointed portion 49 with respect to the valve seat 39.Valve stem 47 carries a piston 52 having labyrinth sealing rings 53 andmovable within the lower, larger diameter portion 54 of the stepped bore51 to actuate the needle valve. Radial ports 55 are provided throughsection 50 at annular recess 56 above the travel of the piston 52 tocommunicate upper bore portion 57 with flow string tubing interior 27whereby pressure of lifted'oil about the valve body 28 is transmitted tothe upper surface 58 of the piston. A compression spring 59 is providedin the upper bore portion 57 centered on the valve stem 47 and engagedbetween the bore step 60 and the piston upper surface 58 to bias thepiston 52 downwardly to thus resiliently assist depression of the valvestem 47 and opening of the valve at 41. The power of spring 59 isselected to provide a desired preload on the piston 52.

Terminal 61 below the piston 52 terminates lower bore portion 54 andthrough radial ports 62 in annular recess 63 and axial passage 64 isadapted to communicate the bore below the piston with annulus 1 1between the outer and inner tubing string 7 and 8 which is power gascontaining so that annulus 11 gas pressure is sensed by the piston 52 atits lower surface 65 in a manner biasing the piston and stem upward.

The valve body 28 is retrievably supported in cylindrical sleeve 66.Latch 31 engaging internal annular recess 67 in the sleeve locks valve28 into place and prevents it from being blown upward out of position.The sleeve 66 is fixed in the tubing section 8a which is pin and boxconnected into the flow string tubing 8. Support ribs 68 center thesleeve 66 and serve to guide the valve body 28 into the sleeve. Plug 69threaded into the lower end of sleeve 66 also supports the valve body 28and in appropriately registered and selected alinement of its ports 45,55 and 62, respectively with upper sleeve apertures 70 intermediatesleeve apertures 71 and lower sleeve apertures 72.

Sleeve apertures 70 and 72 in turn are in open communication with upperrib and tubing apertures 73, 74 and lower rib support and tubingapertures 75, 76. Intermediate sleeve apertures 71 are open to fluidwithin tubing string interior 27. See FIG. 6. Thus piston 52 issimultaneously subjected to a pilot pressure on its upper surface 58from lifted oil through oil from tubing interior 27 entering aperture71, the upper pressure port 55 and upper bore portion 57, and pilotpressure on its lower surface 65 from the pressurized gas supply inannulus 11 entering through tubing aperture 75, rib aperture 76. Sleeveaperture 72, the lower pressure port 62, bore 64 and lower piston bore54. Spring 59 biases the piston downwardly to establish the actuatingforce differential across the piston required to effect operation of thevalve, e.g., 200 pounds.

Middle body and lower body sets of annular seals 77, 78 and 79, 80 areprovided between the valve body 28 and the sleeve 66, with lower seals79, 80 being located between the upper pressure port 55 and the lowerpressure port 62 to fluid tightly seal the body and sleeve between theseports and with middle seals 77, 78 being located between the upperpressure port 55 and the body port 45 to fluid tightly seal the body andsleeve between these ports.

Annular seals 82 and 83 seal off power gas at port 45 from escapingupwardly between valve body 28 and sleeve 66 and comingling withcontrolled gas at 81.

In operation of the invention apparatus and with particular reference toFIGS. 3b and 4, power gas is delivered through annulus 11 to cause fluidto be lifted into inner tubing string 8 as described. Several slugs offluid may be passing through tubing string 8 at one time. The piston 52is arranged to oppositely sense lifted fluid pressure and gas pressureas v described. When these pressures are at a predetermineddifferential, the piston 52 moves down and opens valve opening 41. SeeFIG. 4. Power gas which has entered the valve body 28 through body port45 in open communication with annulus 11 through rib support aperture 74and tubing aperture 73 (see FIG. 5) moves into bore 33 and is jettedupwardly and outwardly by passages 34 through outlets 35 and sleeveopenings 81 into tubing interior 27 up between support ribs 68 to rushpast fishing neck 29 and into the fluid withinthe tubing to lower thedensity thereof or to lighten the same. Upon lowering the density of thefluid, the piston 52 moves upwardly and closes the valve opening 41until a too heavy fluid weight condition again occurs. Production passesupwardly in tubing 8 through reciprocator 9 and out through manifold 84.

The upwardly discharging, retrievable valve of the invention in thedescribed apparatus is believed superior to all other flow valve systemsnow known. The valve is further useful in conjunction with aconventional well gas lifting apparatus shown highly simplified in FIG.7 wherein like parts to FIGS. 1-6 are shown with like numerals with theaddition of e.g., casing 102. Power gas from line 112 is run down theannulus 1 1 1 to packer 190 so as to not exert pressure on the producingzone inward of stratum 104 in casing 105. Density control valveoperating on the differential between fluid in flow string interior 127and annulus 111 between casing 102 and tubing string 108 is admittingits gas in an upwardly jetting direction and serves to lighten thelifted fluid as described above with the lifting gradient within thetubing controllable by the power gas pressure in the annulus 111.Alternatively packer may be omitted and no power gas used where theformation gas pressure is sufficient to lift the well with the help ofthe upwardly directed valve 125, if the formation pressure in stratum104 is sufficient.

I claim:

1. Retrievable valve apparatus for lightening oil being gas liftedthrough a tubing string including a valve body, a valve body mountingsleeve coaxially within the tubing string and radially spaced therefromto define an annular passage, said body having a fishing neck adapted toproject upwardly within the tubing string and valve means carried by thebody for selectively communicating the tubing string interior with apressurized gas supply to inject gas into oil emerging from said passageand upwardly past said fishing neck in response to a predeterminedpressure of oil lifted in the tubing string above the apparatus, saidbody having a port to pass said pressurized gas into the body when thebody is selectively positioned in the string.

2. Retrievable valve apparatus according to claim 1 including also anactuator for the valve means comprising an axially movable pistonresponsive to lifted oil pressure to move downward and to gas supplypressure to move upward, both relative to the fishing neck, whereby saidactuator is responsive to pressure differences between the oil andpressurized gas supply to actuate the valve means.

3. Retrievable valve apparatus according to claim 2 including alsoresilient means arranged to downwardly bias the piston.

4. The combination according to claim 3 in which said valve bodymounting means comprises a sleeve adapted to sealably receive saidapparatus in such fishing neck projecting relation that said neck isaccessible above the sleeve, and port means between said sleeve and saidbody for passage of pressurized gas from without the tubing into thevalve body interior.

5. The combination according to claim 4 including also a verticallyextended bore within the valve body, a valve seat encircling said bore,a valve stem below the bore having a portion normally engaging the valveseat against fluid passage, a valve stem actuator comprising a pistonfixed on the stem and movable axially within the body relative to thefishing neck, a first pressure port for communicating lifted oilpressure around the sleeve to the piston upper surface, and a secondpressure port for communicating gas pressure outside the tubing to thepiston lower surface, said piston being responsive to superior force onits upper surface to unseat the stemhead portion and to permit gas toflow upwardly through the bore in the tubing.

6. The combination according to claim 5 including also compressionspring means centered on the valve stem engaging the piston indownwardly biasing relation.

7. ln apparatus for lifting oil from a well by gas under pres sureincluding spaced concentric tubing strings the inner string of which isadapted to be reciprocably movable within the well, and the outer stringof which defines with said inner string a gas pressure chamber, andmeans carried at the lower end of the inner string adapted to receiveoil in response to string reciprocation to be lifted to the surfacetherethrough by said gas, the improvement comprising retrievable valveapparatus to lighten oil lifted by inner string movement, said apparatuscomprising a retrievable valve body above the oil supply level coaxiallywithin the inner tubing string, a valve body mounting sleeve of lesserdiameter than the inner tubing, mounting sleeve supports extendingbetween the inner tubing string and the mounting sleeve and carrying themounting sleeve for reciprocating movement with the inner tubing stringin spaced relation to the tubing to define an annular passage circularlyof the mounting sleeve within the inner tubing string, said valve bodyhaving an upwardly projecting fishing neck, a central fluid passingvertical bore having an outlet adjacently below the fishing neck, firstport means communicating lifted oil'pressure at the sleeve to said bore,a second port means extending through said sleeve supports forcommunicating gas pressure between the tubing strings to said bore,valve means operatively arranged within said bore to be oppositelyresponsive to lifted oil and gas pressures within the bore and adaptedto pass pressurized gas from between said strings into lifted oil abovesaid annular passage in said inner string, in response to apredetermined pressure of lifted oil and during reciprocating movementof said inner string.

8. Apparatus according to claim 7 in which said valve means includes aneedle valve stem having a pointed portion normally engaging the valveseat against fluid passage; a valve stem actuator comprising a pistonfixed on the stem and movable axially within the body, said first portmeans communicating lifted oil pressure at the sleeve to the pistonupper surface,

said second port means communicating gas pressure between the tubingstrings to the plston, said piston being responsive to superior force onits upper surface to move downwardly to unseat the pointed stem portionand to permit gas from between said tubing strings to flow through thebore and upwardly into the tubing.

9. Apparatus according to claim 8 including also compression springmeans mounted on the valve stem and engaging the piston in downwardlybiasing relation.

10. Apparatus according to claim 9 in which said sleeve supportscomprise upper and lower sets of circularly spaced and radially disposedsupports at vertically spaced locations on said sleeve and centrallywithin the inner tubing string, plural members of each support set beingported and alined to provide fluid communication therebetween.

1. Retrievable valve apparatus for lightening oil being gas liftedthrough a tubing string including a valve body, a valve body mountingsleeve coaxially within the tubing string and radially spaced therefromto define an annular passage, said body having a fishing neck adapted toproject upwardly within the tubing string and valve means carried by thebody for selectively communicating the tubing string interior with apressurized gas supply to inject gas into oil emerging from said passageand upwardly past said fishing neck in response to a predeterminedpressure of oil lifted in the tubing string above the apparatus, saidbody having a port to pass said pressurized gas into the body when thebody is selectively positioned in the string.
 2. Retrievable valveapparatus according to claim 1 including also an actuator for the valvemeans comprising an axially movable piston responsive to lifted oilpressure to move downward and to gas supply pressure to move upward,both relative to the fishing neck, whereby said actuator is responsiveto pressure differences between the oil and pressurized gas supply toactuate the valve means.
 3. Retrievable valve apparatus according toclaim 2 including also resilient means arranged to downwardly bias thepiston.
 4. The combination according to claim 3 in which said valve bodymounting means comprises a sleeve adapted to sealably receive saidapparatus in such fishing neck projecting relation that said neck isaccessible above the sleeve, and port means between said sleeve and saidbody for passage of pressurized gas from without the tubing into thevalve body interior.
 5. The combination according to claim 4 includingalso a vertically extended bore within the valve body, a valve seatencircling said bore, a valve stem below the bore having a portionnormally engaging the valve seat against fluid passage, a valve stemactuator comprising a piston fixed on the stem and movable axiallywithin the body relative to the fishing neck, a first pressure port forcommunicating lifted oil pressure around the sleeve to the piston uppersurface, and a second pressure port for communicating gas pressureoutside the tubinG to the piston lower surface, said piston beingresponsive to superior force on its upper surface to unseat the stemhead portion and to permit gas to flow upwardly through the bore in thetubing.
 6. The combination according to claim 5 including alsocompression spring means centered on the valve stem engaging the pistonin downwardly biasing relation.
 7. In apparatus for lifting oil from awell by gas under pressure including spaced concentric tubing stringsthe inner string of which is adapted to be reciprocably movable withinthe well, and the outer string of which defines with said inner string agas pressure chamber, and means carried at the lower end of the innerstring adapted to receive oil in response to string reciprocation to belifted to the surface therethrough by said gas, the improvementcomprising retrievable valve apparatus to lighten oil lifted by innerstring movement, said apparatus comprising a retrievable valve bodyabove the oil supply level coaxially within the inner tubing string, avalve body mounting sleeve of lesser diameter than the inner tubing,mounting sleeve supports extending between the inner tubing string andthe mounting sleeve and carrying the mounting sleeve for reciprocatingmovement with the inner tubing string in spaced relation to the tubingto define an annular passage circularly of the mounting sleeve withinthe inner tubing string, said valve body having an upwardly projectingfishing neck, a central fluid passing vertical bore having an outletadjacently below the fishing neck, first port means communicating liftedoil pressure at the sleeve to said bore, a second port means extendingthrough said sleeve supports for communicating gas pressure between thetubing strings to said bore, valve means operatively arranged withinsaid bore to be oppositely responsive to lifted oil and gas pressureswithin the bore and adapted to pass pressurized gas from between saidstrings into lifted oil above said annular passage in said inner string,in response to a predetermined pressure of lifted oil and duringreciprocating movement of said inner string.
 8. Apparatus according toclaim 7 in which said valve means includes a needle valve stem having apointed portion normally engaging the valve seat against fluid passage;a valve stem actuator comprising a piston fixed on the stem and movableaxially within the body, said first port means communicating lifted oilpressure at the sleeve to the piston upper surface, said second portmeans communicating gas pressure between the tubing strings to thepiston, said piston being responsive to superior force on its uppersurface to move downwardly to unseat the pointed stem portion and topermit gas from between said tubing strings to flow through the bore andupwardly into the tubing.
 9. Apparatus according to claim 8 includingalso compression spring means mounted on the valve stem and engaging thepiston in downwardly biasing relation.
 10. Apparatus according to claim9 in which said sleeve supports comprise upper and lower sets ofcircularly spaced and radially disposed supports at vertically spacedlocations on said sleeve and centrally within the inner tubing string,plural members of each support set being ported and alined to providefluid communication therebetween.